The invention relates to a cooler for mixtures of crystals and crystallizing liquid in the production of sugar and related products, such products, which during crystallization show a similar behaviour as sugar, including particularly other saccharides, such as fructose and glucose.
In the crystallization of easily soluble materials, the solubility of which increases with increasing temperature, crystallization is often effected by cooling a mixture of crystals and solution. This mixture will in the following be referred to as massecuite.
Such mixtures of crystals and solution frequently have a high apparent viscosity (consistency). This is e.g. the case in the crystallization of saccharose, fructose and glucose. The cooling meets with difficulties because the high viscosity results in a poor transfer of heat and because frequently a layer of crystals grows up on the cooling surfaces, thereby additionally reducing the heat transmission.
The cooling is frequently effected in containers with stirring mechanisms and with a movable or stationary cooling surface, which is cooled by water, air or other cooling media. The cooling is performed either batch-wise or by causing the massecuite to flow continuously through one or more containers provided with cooling equipment. It has been found in practice that the limiting factor in the crystallization process is the obtainment of the sufficient temperature drop, and it is often difficult and expensive to build in the sufficient cooling surface area.
In order to obtain optimum crystallization with maximum yield it has been found by experiment that in the crystallization of the last product in the saccharose production it is useful to obtain a rapid cooling of the massecuite from the temperature of 70.degree.-80.degree. C. at which it is produced to 60.degree. C., whereafter a slower cooling in traditional equipment is advantageous.
Coolers are known in the form of a pipe cooler having substantially vertical pipes through which a fluid is pumped and which opens into chambers at their bottom and top ends and are surrounded by a cooling medium, e.g. circulating water. However, these known coolers are not suitable for the cooling of mixtures of crystals and crystallizing liquids of the type here concerned, because a layer of of crystals is rapidly formed on the inner wall of the pipes, whereby the pipes can easily get clogged.